This invention relates to a control device for an alternating current generator of a vehicle, particularly for controlling the field current of an alternating current generator.
FIG. 2 is a circuit diagram showing the construction of a conventional control device for an alternating current generator of a vehicle. In FIG. 2, reference numeral 1 designates an alternating current generator having an armature coil 101 in a star connection and a field coil 102, and 2, a three-phase full-wave bridge rectifier having three sets of diodes connected to the armature coil 101, a main rectified output terminal 201, an auxiliary rectified output terminal 202 and a grounded output terminal 203.
Reference numeral 3 designates a voltage regulator which controls an output voltage of the alternating current generator to a predetermined value by controlling the field current flowing in the field coil 102, 4, a battery charged by a rectified output of the alternating current generator, 5, a key switch, and 6, a charge display lamp.
Numerals 301 and 302 designate transistors connected in a Darlington pair which interrupt the field current of the generator, 303, a field discharge diode, and 304, a current detecting resistance inserted between the emitter of the transistor 301 and ground, and having a positive temperature coefficient. Numerals 305 and 306 designate voltage dividing resistances for setting a reference voltage, and having a positive temperature coefficient, 307, a comparator for comparing the divided voltage with the potential across resistance 304, and 308, a resistance for initial excitation of which one end is connected to the base of the transistor 302, and the output terminals of the comparator 307 and a comparator 309.
Numerals 310 and 311 designate resistances which divide a reference voltage, and 312 and 313, resistances which divide the voltage of the battery 4. The comparator 309 makes a comparison between these divided voltages. Numeral 314 designates a resistance, 315 and 316, diodes, 317, a Zener diode, and 318, a transistor, which form a reference voltage based on the voltage of the battery 4.
One end of the field coil 102 of the alternating current generator 1 is connected to the collectors of the transistors 301 and 302, and the anode of the field discharge diode 303. The other end thereof is connected to the auxiliary rectified output terminal 202, the cathode of the field discharge diode 303, and the other end of the resistance 308, as well as to the positive pole of the battery 4 whose negative pole is grounded, through the charge display lamp 6 and the key switch 5. The main rectified current output terminal 201 of the rectifier 2 is connected to the positive pole of the battery 4.
Next, an operational explanation will be given, referring to FIG. 2. When the key switch 5 is switched to ON, base currents flow to the transistors 302 and 301 from the battery 4 through the key switch 5, the charge display lamp 6, and the resistance 308, successively. An initial excitation current flows in the field coil 102 when the transistors 302 and 301 are switched ON. When the alternating current generator 1 is driven by an engine, not shown, in this state, power generation starts.
When power is generated, the emitter current of the transistor 301 which is correlated with the field current flowing in the field coil 102, that is, approximately equal to the field current, flows in the current detecting resistance 304. Therefore, a potential difference is generated across the resistance 304. This potential difference is compared with a junction point potential of the voltage dividing resistances 306 and 305 by the comparator 307. When the potential difference becomes higher than the junction point potential due to an increase of the field current, the output of the comparator 307 becomes "L" level, which switches the transistors 302 and 301 to OFF, and cuts off the field current. When the transistors 301 and 302 are switched to OFF, the output of the comparator 307 is reversed to the "H" level again, which switches the transistors 302 and 301 to ON again, and resumes the field current in the field coil 102.
By repeating the above operation, the field current is controlled so that it is restricted to a predetermined value, and the output voltage of the alternating current generator is controlled to a predetermined value. The alternating current signal generated by the alternating current generator 1, is rectified to a direct current by the rectifier 2, charges the battery 4 and activates the field coil 102.
When the charged voltage of the battery 4 reaches a predetermined value or more, the comparator 309 outputs an "L" level, which switches the transistors 302 and 301 to OFF. Furthermore, the circuit composed of the zener diode 317, the transistor 318 and the like, operates to maintain constant the reference voltage based on the voltage of the battery 4.
In the conventional control device constructed as above, the current detecting resistance 304 is provided with a low value of 10 to 100 m.OMEGA. to reduce the loss thereby. In a hybrid IC, generally, a conductor resistance of Ag/Pd is utilized as an electrode material. On the other hand, the voltage dividing resistances 305 and 306 forming a reference voltage for comparison, have a positive temperature coefficient of about 200 PPM. Since the voltage dividing resistances 305 and 306 are provided on opposite sides of the voltage junction point, which compensates for any influence by temperature, the voltage detecting level does not vary with temperature. However, the conductive material utilized as the temperature detecting resistance 304, has a positive temperature coefficient of about 500 PPM. Therefore, with an increase in temperature, the operating current value for the "L" level of the comparator 307 is decreased, and a negative temperature gradient is provided in a field current restricting value.